Studies in the human will be extended to the analysis of low-renin hypertension into etiological subgroups, and the evaluation of the renin-aldosterone changes in abnormal pregnancy. If possible, angiotensin antagonists will be applied in non-pregnant subjects to determine the role of angiotensin II in aldosterone secretion and in certain forms of hypertension. Angiotensin II receptors of the adrenal gland will be further employed to study the conformational requirements for receptor binding and target cell activation, utilizing a number of agonist and antagonist analogues of angiotensin II. The mechanisms by which angiotensin II, ACTH and potassium stimulate aldosterone production will be further explored in dispersed adrenal cells. The relationship of receptor occupancy with membrane- associated enzymes and cyclic nucleotide turnover will be analyzed in more detail, and the possible role of sodium-potassium activated ATP'ase in the action of angiotensin will be investigated.